METHOD FOR DRY ETCHING Al2O3 FILM

ABSTRACT

The invention provides a dry etching method for processing a wafer having an Ru film formed on a thick Al 2 O 3  film to be used for a magnetic head, capable of realizing high selectivity. In the etching of a wafer having disposed on an NiCr film 15 an Al 2 O 3  film 14, an Ru film 13, an SiO 2  film 12 and a resist mask 11, the Ru film 13 is etched via plasma using a processing gas containing Cl 2  and O 2  (FIG.  1 ( c )), and thereafter, the Ru film 13 is used as a mask to etch the Al 2 O 3  film 14 via plasma using a gas mixture mainly containing BCl 3  and also containing Cl 2  and Ar (FIG.  1 ( d )).

The present application is based on and claims priority of Japanesepatent application No. 2007-249429 filed on Sep. 26, 2007, the entirecontents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for dry etching a multilayeredfilm, and more specifically, relates to a dry etching method forprocessing an alumina (Al₂O₃) film having a thickness of 200 nm to 1000nm arranged on a nickel chrome (NiCr) alloy film, in which a ruthenium(Ru) film is used as mask to process the Al₂O₃ film with highselectivity to obtain a perpendicular process shape.

2. Description of the Related Art

When processing Al₂O₃ films having a thickness of 200 nm to 1000 nm usedfor forming magnetic heads in a dry etching apparatus, a nonvolatilematerial such as NiCr alloy film or the like is used as the maskmaterial to achieve the required selectivity. This NiCr alloy film isnonvolatile, and is difficult to process via dry etching, so it isconventionally processed via milling. However, along with theminiaturization of the processing object, milling processes have becomemore and more difficult due to drawbacks of accuracy and processingrate. Therefore, studies are now being performed to process the maskmaterial and the Al₂O₃ film via dry etching.

In other words, it is necessary to find a mask material that enables themask and the Al₂O₃ film to be dry-etched and has high selectivity withrespect to the Al₂O₃ film.

FIG. 5 is referred to in describing a processing method using an NiCralloy film as mask material.

FIG. 5( a) is a cross-sectional view of a wafer prior to the etchingprocess. The wafer includes, from the upper layer in the named order, apatterned resist mask 11, an upper layer NiCr alloy film 15, an Al₂O₃film 14 and a lower layer NiCr alloy film 15. At first, the millingprocess of the upper layer NiCr alloy film 15 performed under conditionsusing a fluorine-based gas causes the surface layer portion of the Al₂O₃film 14 to be etched for approximately 80 nm in a tapered shape, andthus, it becomes difficult to fine-process the NiCr alloy film (FIG. 5(b)). Next, when the Al₂O₃film 14 is dry-etched in a low pressure rangeusing a gas mixture containing boron trichloride (BCl₃), chlorine (Cl₂)and argon (Ar), the etching proceeds with the surface layer portion ofthe Al₂O₃ film 14 still tapered by the milling process, so theprocessing shape of the Al₂O₃ film will be tapered and could not beetched perpendicularly (FIG. 5( c)).

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method for etchingthick Al₂O₃ films used in magnetic heads, wherein the method enables toetch the mask material via dry etching with high etching selectivity.

Furthermore, the present invention provides a method for dry-etching theaforementioned mask material and Al₂O₃ film.

One characteristic feature of the present invention is to use an Ru filmthat could be dry-etched using a gas mixture containing Cl₂ and O₂ asthe mask material of the Al₂O₃ film.

The ruthenium film is dry-etched using a gas mixture containing Cl₂ andO₂, and the Al₂O₃ film could be dry-etched using a gas mixture mainlycontaining BCl₃ and also containing Cl₂ and Ar.

Moreover, in order to realize fine processing, a BARC film can bedeposited as anti reflection film on the upper layer, by which the BARClayer can be trimmed so as to control the wiring dimensions.

According to the present invention, an Ru film is used as the maskmaterial of the Al₂O₃film 14 since it has high selectivity, so that themask material and the Al₂O₃ film can be processed via dry etching,enabling fine-processing of the Al₂O₃ film and perpendicular processingof the Al₂O₃ film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating an etching methodaccording to a preferred embodiment of the present invention;

FIG. 2 is a view illustrating the mask material selectivity according tothe present invention;

FIG. 3 is a cross-sectional view showing the configuration of an etchingapparatus;

FIG. 4 is a cross-sectional view illustrating an etching methodaccording to a preferred embodiment of the present invention; and

FIG. 5 is a cross-sectional view illustrating an etching methodaccording to the prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention enables to dry-etch mask materials and Al₂O₃ filmsby selecting Ru films having high selectivity as the mask material forprocessing thick Al₂O₃ films used for magnetic heads.

Details on how the mask material was discovered according to the presentinvention will now be described.

Al₂O₃ films, or alumina films, can be dry etched using a gas mixturemainly containing BCl₃ and further containing Cl₂ and Ar, and a knownmethod for etching Al₂O₃ films realizes main etching and over etching ofthe Al₂O₃ film by varying the bias power applied to the sample. Theetching rate of the Al₂O₃ film when bias power is varied was 78.1 nm/minwhen a low bias of 30 W was applied and 159.8 nm/min when a high bias of200 W was applied.

The mask material for processing the Al₂O₃ film must have a highselectivity, which is computed by the aforementioned Al₂O₃ film etchingrate/mask material etching rate.

Under the same conditions using the aforementioned gas mixture of BCl₃,Cl₂ and Ar, the relationship of the selectivities of Al₂O₃ film to thevarious materials is shown in FIG. 2.

The selectivity of the Al₂O₃film etching rate to mask material etchingrate with varied bias power applied was 1.69 or smaller when a resistfilm, an SiO₂ film, a tantalum film or a TiN film was used, and on theother hand, the selectivity of the Al₂O₃ film etching rate to Ru filmetching rate using an Ru film with varied bias power applied was 2.02when a high bias of 200 W was applied and 19.5 when a low bias of 30 Wwas applied.

That is, since the resist film, the SiO₂ film, the tantalum (Ta) filmand the titanium nitride (TiN) film have a low selectivity of 0.63 to1.69, respectively, with respect to the Al₂O₃ film, the films must bedeposited sufficiently thick as mask material for the Al₂O₃ film, andthe aspect ratio becomes high, so that it becomes difficult to processthe Al₂O₃ film perpendicularly. Therefore, it is difficult to selectthese materials to form a mask for the thick Al₂O₃ film.

On the other hand, the Ru film can be dry-etched using a gas mixture ofCl₂ and O₂, and the etching rate of the Al₂O₃ film was 2.7 nm/min whenbias power of 150 W was applied.

Thus, according to the present invention, the Ru film was selected asthe mask material for the Al₂O₃ film, since it has high selectivity withrespect to the Al₂O₃ film and since the etching of the Al₂O₃ film, orfilm to be etched, proceeds very slowly.

Next, the mask material for dry-etching the Ru film was selected. The Rufilm can be dry-etched using a gas mixture containing Cl₂ and O₂. Theetching rate of each material was confirmed with a bias power of 150 Wapplied. At this time, the etching rate of the resist film was 1957.5nm/min and the etching rate of the SiO₂ film was 14.3 nm/min.

Therefore, according to the present invention, a silicon oxide (SiO₂)film with a low etching rate was used as the mask material for the Rufilm in dry-etching the Ru film using a gas mixture containing Cl₂ andO₂.

Now, a preferred embodiment of the method for dry-etching theaforementioned Al₂O₃film and the mask material will be described indetail with reference to FIG. 1 illustrating a cross-sectional view of awafer, or sample.

FIG. 1( a) is a view showing the cross-section of a wafer which is theobject of the etching process according to the present invention. Thewafer is a multilayered material including, from the upper layer in thenamed order, a patterned resist mask 11, a hard mask, or SiO₂ film, 12which is the material to be etched, a ruthenium film 13, an Al₂O₃ film14, and an NiCr alloy film 15 which is a base stopper.

The resist film 11 patterned via the dry etching method using a gascontaining fluorine is used as a mask to etch the SiO₂ film 12 of theabove-described wafer. By this process, the SiO₂ film 12 is patterned,which constitutes the mask for the Ru film 13 (FIG. 1( b)).

In a second step, the patterned SiO₂ film 12 and the patterned resistfilm 11 are used as a mask to dry-etch the Ru film 13. At this time, bydry-etching the Ru film 13 under conditions using a gas mixturecontaining Cl₂, O₂ and Ar, the etching of the lower layer Al₂O₃ film 13proceeds only very slowly, so the etching process could be performedrealizing a substantially perpendicular taper angle of the side surfaceof the Ru film 13 and the surface of the Al₂O₃ film 14 (FIG. 1( c)).

In a third step, the patterned Ru film 13 and the patterned SiO₂ film 12formed in the second step is used as a mask to etch the Al₂O₃ film 14.At this time, by dry-etching the Al₂O₃ film under conditions using a gasmixture mainly containing BCl₃ and also containing Cl₂ and Ar, the Al₂O₃film 14 could be processed perpendicularly using the perpendicularlyprocessed Ru mask 13 (FIG. 1( d)).

The dry etching of the Al₂O₃ film in the third step is performed underthe following conditions: a ratio of BCl₃:Cl₂:Ar=40:10:50, a pressure inthe low pressure range of 0.3 Pa to 0.8 Pa, and a wafer temperature of300 degrees or lower which does not cause burning of resist.

Moreover, the tapered angle of the processed shape can be approximatedto a perpendicular shape by increasing the bias power and increasing thewafer temperature.

FIG. 3 is used to describe an example of the structure of a plasmaetching apparatus to which the present invention is applied. In FIG. 3,the plasma etching apparatus includes a high-frequency power supply 101,an automatic matching unit 102, an inductively-coupled coil 103, avacuum reactor 104, a gas supply unit 106, a vacuum pump 107, a samplestage 109, a bias power supply 110, a high-pass filter 111, a directcurrent power supply 113, and a low-pass filter 114. The vacuum reactor104 includes a discharge unit 104 a formed of an insulating material anda grounded processing unit 104 b. An insulating film 112 formed forexample of ceramics is arranged on the surface of the sample stage 109,wherein a heater 115 and a refrigerant flow path 116 is disposed thereinso as to control the temperature of a sample 108 to thereby control theprocessing thereof. Further, an antenna 118 connected to ahigh-frequency power supply 101 is arranged on the upper portion of thedischarge unit 104 a in the atmospheric area, which is connected via aload.

The plasma etching apparatus supplies high frequency current to theinductively coupled coil 103 from the high-frequency power supply 101via the automatic matching unit 102, and causes plasma to be generatedin the vacuum reactor 104. The vacuum reactor 104 includes a dischargeunit 104 a formed of an insulating material and a grounded processingunit 104 b. Etching gases such as Cl₂ and BCl₃ are introduced via thegas supply unit 106 to the vacuum reactor 104, and the gases are thenevacuated through the vacuum pump 107.

A sample 108 is placed on the sample stage 109. In order to increase theenergy of ions being incident on the sample 108, a bias power supply 110which is a second high-frequency power supply is connected to the samplestage 109 via a high-pass filter 111. An insulating film 112 formed forexample of ceramics is arranged on the surface of the sample stage 109.Further, a direct current power supply 113 is connected to the samplestage 109 via a low-pass filter 114, which holds the sample 108 onto thesample stage 109 via electrostatic chuck.

Further, a heater 115 and a refrigerant flow path 116 are provided inthe sample stage 109 so as to control the temperature of the sample 108and thereby control the processing thereof.

The plasma generating mechanism of the plasma etching apparatus forcarrying out the present invention is not restricted to aninductively-coupled plasma, and other low-pressure plasma generatingmechanisms can be used. For example, the present invention can beapplied for example to apparatuses having an ECR (electron cyclotronresonance) plasma generating mechanism, a magnetron RIE plasmagenerating mechanism or a helicon wave plasma generating mechanism.

The SiO₂ film 12, the Ru film 13 and the Al₂O₃ film 14 can be processedconsistently in the same chamber. It is also possible to use separatechambers for etching the SiO₂ film 12 and Ru film 13 and for etching theAl₂O₃ film.

Next, the second embodiment of the present invention will be describedwith reference to FIG. 4. The second embodiment is an example in which aBARC is disposed between the resist mask and the SiO₂ hard mask in thewafer structure shown in FIG. 1. FIG. 4( a) is a view showing thecross-section of a wafer which is the object of the etching processaccording to the present invention. The wafer is a multilayered materialincluding, from the upper layer in the named order, a patterned resistmask 11, a BARC film 16 which is an anti reflection film, a hard mask,or SiO₂ film, 12 which is the material to be etched, an Ru film 13, anAl₂O₃ film 14, and an NiCr film 15 which is abase stopper.

As the first step, the BARC film 16 is etched using fluorine-based gas,by which the BARC film 16 is trimmed, and the wiring dimension can becontrolled (FIG. 4( b)). Thereafter, the resist film 11 and the BARCfilm 16 patterned via the dry etching method using gas containingfluorine is used as a mask to etch the SiO₂ film 12. By this process,the BARC film 16 and the SiO₂ film 12 are patterned, creating a mask forthe Ru film 13 (FIG. 4( c)). Then, the resist mask 11, the BARC film 16and the SiO₂ film 12 are used as a mask to dry-etch the Ru film 13. Atthis time, by dry-etching the Ru film 13 using a gas mixture containingCl₂ and O₂, the etching of the lower Al₂O₃ film 13 layer proceeds onlyvery slowly, so the etching process could be performed realizing asubstantially perpendicular taper angle of the side surface of the Rufilm 13 and the surface of the Al₂O₃ film 14 (FIG. 4( d)). The resist 11and the BARC film 16 arranged above the SiO₂ film 12 are removed duringthis process.

The patterned Ru film 13 and the patterned SiO₂ film 12 formed duringetching of the Ru film 13 are used as the mask to etch the Al₂O₃ film14. At this time, by dry-etching the Al₂O₃ film using a gas mixturemainly containing BCl₃ and also containing Cl₂ and Ar, the Al₂O₃ film 14could be processed perpendicularly using the perpendicularly processedRu mask 13 (FIG. 4( e)). The dry etching of the Al₂O₃film according tothis process is performed under the following conditions: a ratio ofBCl₃:Cl₂:Ar=40:10:50, a pressure in the low pressure range of 0.3 Pa to0.8 Pa, and a wafer temperature of 300 degrees or lower which does notcause burning of the resist.

1. A method for dry etching an Al₂O₃ film of a sample having a rutheniumfilm arranged on an Al₂O₃ film, comprising: a first plasma etching stepfor etching a ruthenium film using a processing gas containing chlorineand oxygen; and a second plasma etching step for continuously using theruthenium film as a mask to etch the Al₂O₃ film using a gas mixturemainly containing boron trichloride (BCl₃) and also containing chlorineand argon.
 2. The method for dry etching an Al₂O₃film according to claim1, wherein the sample includes an SiO₂ film as a mask arranged on theruthenium film; and the method comprises a mask plasma processing stepfor trimming the SiO₂ film via an etching process using fluorine-basedgas to control the wiring dimension prior to performing the first plasmaetching step.
 3. The method for dry etching an Al₂O₃film according toclaim 1, wherein the sample includes an SiO₂ film as a mask arranged onthe ruthenium film and a BARC film as anti reflection film arranged onthe SiO₂ film; and the method comprises a mask plasma processing stepfor trimming the SiO₂ film via an etching process using fluorine-basedgas to control the wiring dimension prior to performing the first plasmaetching step; and a BARC film plasma processing step for trimming theBARC film via an etching process using fluorine-based gas to control thewiring dimension prior to the mask plasma processing step.